House Republicans passed a short-term transportation reauthorization bill Tuesday, openly defying an influential conservative group that had made the measure a litmus test for conservative purity.

Although Heritage Action for America had designated the extension of surface and air transportation programs as a “key vote” — which means the vote will be used to score Members’ conservative bona fides before next year’s election — Republicans not only supported the bill but even passed it by voice vote.

Leadership aides declined to comment on the vote or why they decided to pass it by voice vote.

A conservative activist downplayed the passage of the bill, arguing that it appears the decision to move the bill Tuesday “happened so fast after leadership figured” that it had the votes for passage, and “it seems it may have caught some [conservatives] off guard.”

But a veteran GOP House aide familiar with the situation rejected that explanation.

The aide said Majority Whip Kevin McCarthy’s (R-Calif.) office sent out several whip notices to Members and staff throughout the day Tuesday notifying lawmakers that the bill was on the floor and that a vote was expected. Additionally, Republicans used the full 40 minutes of debate time, the aide explained, saying Members had more than enough time to know it was on the floor.

“It shouldn’t have been a surprise to anyone when the timing of the vote was,” the aide added.

Still, passage of the bill with no opposition is remarkable for a number of reasons.

Scrapping a roll call vote on the bill appears to have been an open act of defiance against an influential conservative group by leadership, which has clashed with the group in the past. In fact, Heritage Action opposed the debt deal passed in August, as well as other measures.

But in the past, leadership has been careful to at least give a cursory nod to conservative opponents.

For instance, during this summer’s debt limit deal, leadership used legislative vehicles like the Cut, Cap and Balance bill, which had no chance of passing the Democratic-controlled Senate, to demonstrate its commitment to conservative values even as it was negotiating a compromise with Democrats.

Additionally, earlier this year Heritage Action teamed up with conservatives in the House to scuttle a planned vote on the Trade Adjustment Assistance program, a favored measure among Democrats but vehemently opposed by conservatives. Heritage Action’s decision to call the bill a key vote, along with a last-minute push by the Republican Study Committee against it, forced leadership to pull it from the floor when rank-and-file Members abandoned the measure in droves.

Still, Speaker John Boehner (R-Ohio), Majority Leader Eric Cantor (R-Va.) and McCarthy have been willing to ignore the demands of interest groups once they have settled on legislation that they believe will garner strong GOP support, such as the continuing resolution this spring and the final debt deal.

Perhaps more striking is the fact that rank-and-file Members, including members of the Republican Study Committee, did not object to passing the bill by voice rather than using a roll call vote.

Voice votes are rarely used in the sharply divided House and are almost never applied to massive spending authorization bills like the transportation package. Traditionally, anytime a powerful interest group such as Heritage Action opposed to a measure key-votes it, at least one Member will object to using a voice vote to pass the bill, forcing a roll call vote to put his colleagues on record.

The use of key votes to keep track of lawmakers’ ideological purity has long been a source of tension between outside groups and elected officials, particularly for freshmen who were sent to Washington “to stop President Obama’s policy agenda,” Heritage Action Communications Director Dan Holler said.

“If you look at what happened on our scorecard, a lot of these guys got bumped down” as a result of votes on the CR this spring and the debt bill, Holler added.

He also warned that “when people around the country figure out what’s going ... they’re going to be frustrated.”